The present invention relates to formworks for round or polygonal constructions, especially to formworks which are free of tensioning points and comprise a formwork face or sheathing having an adjustable curvature or circumference and comprising a chain of booms which are spaced apart from the formwork face and have individual boom portions, the boom portions being adapted to pivot relative to one another so as to alter their mutual angular positions by means of joints and being fixable in selected angular positions when the adjustment of the formwork face is completed.
A similar formwork is disclosed in German printed patent application No. 21 40 638. The individual boom portions are coupled to each other by joints about which they can be adjusted relative to one another. A threaded bolt extending in spaced relationship to the joint serves for adjustment and fixing. In order to adjust the formwork to a selected circumference or curvature, the boom portions must first be adjusted and fixed in their relative angularity and only thereafter can the formwork face or sheathing be applied. Therefore, the assembly of such formworks is time-consuming. The play in the individual joints, and particularly the combined play in all of the joints, may lead to considerable deviation from the desired angular position.
German Auslegeschrift No. 28 05 612 discloses a formwork wherein the faces of the individual boom portions again feature connecting joints flanked by screw bolts with threads for adjusting the angular positions of the boom portions. Thus, if installed carefully, the play in the joints can be eliminated. However, the installation is time-consuming and the relative positions of individual boom portions must be adjusted before the formwork face or sheathing can be applied.